FIG. 2 illustrates first and second spiral bodies 1 and 2 in a scroll fluid machine disclosed in Japanese Patent Laying-Open No. 60-252102. In FIG. 2, the first spiral body 1 corresponds to a fixed scroll and the second spiral body 2 corresponds to a movable scroll.
As shown in FIG. 2, a discharge port 3 is provided in the vicinity of winding starting ends of the first and second spiral bodies 1 and 2 in order to discharge compressed refrigerant. A thickness t4 of the first spiral body 1 located in the vicinity of discharge port 3 is defined to be larger than a thickness t5 of a winding finishing end of the first spiral body 1. The second spiral body 2 is similarly shaped.
The increased thickness t4 of the winding starting ends of the first and second spiral bodies 1 and 2 in the vicinity of discharge port 3 can enhance the strength of the portion near the winding starting ends of the first and second spiral bodies 1 and 2, and prevent leakage of refrigerant occurring at the central portion.
However, the increased thickness at the central portion of the spiral bodies causes a problem described below. Using FIG. 3, the problem is described. FIG. 3 shows a relation between pressure and volume in a compression chamber formed by the first and second spiral bodies 1 and 2, where P1 and P1' represent the pressure in the compression chamber when refrigerant is discharged, P2 represents the pressure in the compression chamber when the refrigerant is taken in, V1 represents the volume of the compression chamber when the refrigerant is taken in, and V2 represents the volume of the compression chamber when the refrigerant is discharged.
Since the thickness t4 of the winding starting ends of the first and second spiral bodies 1 and 2 is increased as described above, an opening area of discharge port 3 is small unless the first and second spiral bodies 1 and 2 are enlarged. Discharge resistance of the refrigerant from discharge port 3 accordingly increases to excessively raise the pressure in the compression chamber from P1 to P1', for example, as shown in FIG. 3 when the refrigerant is discharged, which is referred to as phenomenon of excessive compression. As a result, an extra work W becomes necessary, leading to increase in loss.